Various techniques and equipment have been utilized for testing the integrity of fluid barriers and seals. U.S. Pat. Nos. 3,795,138 and 3,934,464 disclose techniques and equipment for testing the bursting strength of plastic pipe. U.S. Pat. No. 4,077,250 discloses techniques for determining the bursting pressure of metal pipe. U.S. Pat. Nos. 4,416,147 and 4,413,501 disclose hydrostatic testing or pressure testing techniques for determining the integrity of a pipe joint and a flexible tubing, respectfully. U.S. Pat. No. 3,872,713 discloses techniques for detecting a tubing hanger leak, and more specifically for testing a subsea wellhead seal assembly which includes monitoring the diameter of the inner bore of the pipe string below the seal assembly.
Those skilled in the art of oilfield tubulars and the threaded connections for those tubulars recognize that, regardless of the theoretical integrity of the oilfield tubular and/or the theoretical integrity of the threaded connection of coupled tubulars forming the tubing string, the actual integrity of the tubular connection practically must be determined at the oilfield drilling rig or pipe rack site where the connection is made-up. The equipment and techniques for performing this function accordingly must be rugged yet highly reliable.
Many oilfield tubular connections currently are not field tested after make-up at the well site due to the time and expense associated with the testing procedure. Nevertheless, the costs and delays associated with correcting a leaking connection once positioned downhole favor increased use of techniques and equipment to sequentially test each threaded connection at the well site immediately subsequent to the make-up operation. Moreover, the benefits of testing each threaded connection increase with increased use of oilfield tubulars in deep wells, with the increased use of connections adapted for withstanding higher pressure differentials and/or corrosive downhole fluids, and with the increased use of threaded connections utilizing multiple and increasingly sophisticated seals.
Various techniques have thus been devised specifically for testing the integrity of each oilfield tubular connection made up at the well site. The interior of a tubular may be pressurized, using packers to isolate the tubular stand to be tested, as disclosed in U.S. Pat. No. 3,800,596. Once the interior of the tubular connection has been pressurized, this interior pressure may be monitored by a conventional gauge, and the decrease in pressure over time may thus indicate a leak of the threaded connection, as disclosed in U.S. Pat. No. 3,795,138. Alternative techniques for detecting a leak of a pressurized oilfield connection utilize a gas detector or sniffer, as disclosed in U.S. Pat. Nos. 4,926,680 and 4,998,435. U.S. Pat. No. 4,081,990 discloses additional technology for conducting a hydrostatic pressure test on an oilfield tubular. U.S. Pat. No. 4,548,069 discloses a relatively complex testing tool for pressure testing the interior of a oilfield tubular connection.
Others skilled in the art of testing the integrity of oilfield tubular threaded connections have encouraged the use of equipment and techniques which pressurize the exterior of the oilfield tubular connection. U.S. Pat. Nos. 3,921,437 and 4,185,492 disclose complicated devices for forming a sealed chamber exterior of the connection, so that this chamber can be pressurized and a pressure drop in this chamber detected to indicate a leak in the oilfield tubular connection. U.S. Pat. No. 5,209,105 discloses techniques for both externally and internally testing a tubular connection, and particularly discloses a technique for conducting a low pressure test to indicate leakage of a connection seal which might not leak at a higher test pressure.
Because of the difficulties and cost associated with reliably forming a pressurized fluid chamber exterior of the threaded connection, most oilfield tubular connections are tested utilizing high pressure internal of the connection, with the leak detection equipment being associated with either a drop in interior fluid pressure, or with the visual or chemical detection of fluids escaping externally from the made-up connection.
In spite of the advancements made in pressure testing the integrity of oilfield connections at the well site, significant problems has severely limited the acceptance of this procedure in the oil and gas exploration and recovery industry. Many oilfield tubular threaded connections rely upon multiple seals within each connection, with each seal being capable of independently sealing the connection, at least for the relatively short time period of a test. Accordingly, a metal-to-metal shoulder seal and a tapered flank seal within the connection may leak, but the O-ring or other elastomeric seal downstream from the shoulder and flank seals may reliably contain the test pressure. This back-up arrangement of multiple seals may be desirable to obtain an extended life for the connection, but adversely affects the connection integrity test. If the O-ring seal holds during the test, the connection will be placed downhole, where the high temperature and corrosive downhole fluids can pass by the failed shoulder and flank seals to deteriorate the O-ring seal, thereafter causing a connection sealing failure.
Another significant problem with prior art techniques for testing oilfield tubular connection integrity relates to the substantial time required to reliably conduct an effective test. For example, even if both the metal-to-metal flank seal and the downstream O-ring seal of a connection leak during a test, the threads downstream from the O-ring seal may form a temporary seal which prevents the detection of a fluid leak for a time period of approximately 30 minutes or more. Accordingly, a slow leak past both the flank seal and the O-ring seal will spiral slowly through the interstices between the mating threads, with the pipe dope or other thread lubricant preventing the rapid escape of fluids outwardly from the connection during the test period. Those skilled in the art will appreciate that the cost associated with making up and testing each oilfield connection at the well site seldom allows this much time to be expended trying to detect a leaking connection. Accordingly, tubular connections with one or more failed seals are frequently passed through inspection, and are subsequently discovered when the repair and downtime expenses associated with correcting the failed connection are extremely high.
Other problems associated with the equipment used to test the integrity of oilfield tubular threaded connections relates to the high cost and expense associated with the testing procedure itself. Equipment capable of reliably testing threaded connections in a laboratory environment often cannot be reliably used at a well site, where the environment changes drastically, where the made-up connection may be externally dirty, and where the test operator may not be properly trained in the use of the test equipment. If the tubular connection is internally pressurized, the exterior of the connection frequently must be manually cleaned so that the gas detection or other test equipment will be able to detect the escape of fluids from the connection. Other problems associated with prior art test procedures relate to the subjectivity typically required by the test operator to determine if the connection is reliably made up.
The disadvantages of the prior are overcome by the present invention, and improved methods and apparatus are hereinafter disclosed for easily and reliably testing the integrity of an oilfield tubular threaded connection at a well site, thereby substantially increasing the reliability of the downhole connection and thereby reducing the overall cost of the hydrocarbon exploration and recovery operation.